Ferromagnetic material and method of making the same



United States Patent Ofiice 3,l00,l04 Patented Aug. 6, 1963 3,100,194FERRQMAGNETHC MATEREAL AND METHGD F MAKlNG THE SAME Cornelis Martinusvan der Burgt and Elias Put, Eludhoven, Netherlands, assignors to NorthAmerican Philips Company, Inc, New York, N.Y., a corporation of DelawareN0 Drawing. Filed Dec. 29, 1958, Ser. No. 783,126 Claims priority,application Netherlands Jan. 15, 1953 16 Claims. (Cl. 252-625) Thisinvention relates to ferromagnetic materials more particularly forpiezornagnetic vibrators and to methods or making the same.

Such vibrators are useful for converting electrical energy intomechanical energ for example, ultrasonic vibrations, and conversely (seefor example Philips Technical Review, 18, 285-298, 1956/57). For thisuse it is desirable that the material have a maximum electromechanicalcoupling coefiicient and maximum mechanical tensile strength, while themagnetic and mechanical losses must be low and consequently the magneticand mechanical quality factors must be high.

While certain ferromagnetic materials, e.g. nickelcopper ferrites andnickel-cobalt territes, exhibit piezomagnetic properties, theirelectromechanical coupling coefficients are low, viz. less than about0.20. Similarly, a nicke-cobalt ferrite in which a portion of the ironhas been replaced by chromium, also known to exhibit piezomagneticproperties, has been found to be rather inefiicient, particularly whenused in a piezomagnetic vibrator.

It is a principal object of our invention to provide a new and novelmaterial having piezomagnetic properties which has a largerelectromechanical coupling coeificient and is more efficient inconverting mechanical to electrical energy and vice versa.

It is another object of our invention to provide a method of making apiezomagnetic material having a larger electromechanical couplingcoefiicient.

A still further object of our invention is to provide a new and novelpiezomagnetic material which not only exhibits a largerelectromechanical coupling coefiicient but which also has a maximummechanical tensile strength.

Another object of our invention is to provide a new and novel materialexhibiting not only a larger electromechanical coupling coefiicient andmaximum mechanical tensile strength but also low magnetic and mechanicallosses.

These and rurther objects of our invention will appear as thespecification progresses.

In accordance with our invention, this new and novel ferromagneticmaterial which exhibits piezomagnetic properties with a largeelectromechanical coupling coeificient, w losses and high mechanicalstrength, consists of crystals having spinel structure having acomposition corresponding to 29 to 47 mol percent NiO 3 to 20 molpercent CuO 0.5 to 2 mol percent 000 50 to 52 mol percent Fe O In apreferred embodiment of our invention we have found that compositionscorresponding to 35 to 43 mol percent Nil) 6 to 14 mol percent CuO 0.8to 1.4 mol percent C00 50 to 52 mol percent Fe O show the highest valuesof the electromechanical coupling coefiicient. Moreover, the nickeloxide and the copper oxide can be replaced in proportional amounts by atmost 10 mol percent of ZnO.

Our invention also relates to bodies consisting of the said material andto piezomagnetic vibrators containing vibrator bodies which consist ofthe said material and must be made to vibrate by magnetic or acousticalternating fields.

The materials in accordance with the invention have values of theelectromechanical coupling coefficient substantially exceeding 0.20, thevalues or the mechanical quality factor exceeding 2000. Furthermore, thevalues of the magnetic losses and of the porosity are so low that thematerials. can be used to advantage in piezomagnetic vibrators. As isknown, a low value of the porosity is required for a high mechanicaltensile strength and for a high erosion resistance. The term erosion asused herein is meant to be understood as the damage to the radiatingsurface of the vibrator owing to cavitation at high acousticintensities. The absolute values of the iongitudinal saturationmagnetostriction of the materials exceed 20 10- The materials inaccordance with our invention are produced by sintering, at atemperature between 1000 C. and 1400 C., a finely powdered mixture ofnickel oxide, copper oxide, cobalt oxide, iron oxide and the requiredzinc oxide, which oxides can entirely or partly be replaced by compoundswhich On heating are converted into these oxides. Preferably sinteringis perifiormed at a temperature between 1200 C. and 1300 C. The mixtureis preferably heated in air or oxygen but other at mospheres such asnitrogen, car-hon dioxide, etc. may be employed. The latter temperaturesare lower [than the temperatures at which in the known materials,optimum piezomagnetic properties are obtained.

It is essential that the materials in accordance with our inventioncontain at least 50 mol percent of Fe O although larger amounts arepermissible since materials which contain less than 50 mol percent of R0 exhibit large mechanical and magnetic losses which would be a seriousdisadvantage to their application in piezornagnetic vibrators. Amounts.of Fe O in excess of 50 mol percent may result in a lowering of theresistivity of the material which is not detrimental to the desiredpiezomagnetic properties.

The following example is illustrative of the method employed inpreparing the compositions specified in the table in which lists. theproperties of a number of examples of material according to ourinvention.

Example A mixture of nickel oxide, copper carbonate, cobalt ball millfor 18 hours and subsequently prefired at 950 C. in air for 4 hours. Thereaction product was ground in a ball mill with water for 18 hours andafiter drying a small amount of an organic hinder, was added to theproduct which subsequently was pressed to form rings and rods which Weresintered in oxygen at the temperatures given in the following table for2 hours.

The following table indicates the composition of the initial mixture,the sintering temperature and properties of the sintered rings. In theheading of the table p is the porosity which is equal to where d is theX-ray density and d the density,

p is the resistivity in ohms om.,

3 n is the initial permeability at 30 kc./s., tan 6 is the associatedloss factor which is equal to is equal to 1 I (as) is the imaginary partof E is the modulus of elasticity at constant magnetic field strength.With the exception of Q (ring) all e se quantities are materialquantities: in \the values given for Q (ring) the bearing losses of thering are allowed for. Since the value of Q measured on a rodsubstantial-1y is a material quantity, the value of Q (m1) is givenalso. Since magnetic vibrators can be used in baths having temperaturesmaterially exceeding room temperature, or some preparations the valuesof k and of Q (mg) at 50 C. are given. The longitudinal saturationmagnetostriction at room temperature of all these preparations liesbetween 25 X10 and 30 10 where is the real part and properties andconsisting essentially of crystals having a spinel structure and acomposition corresponding to about 35 to 43 mol percent of NiO, about 6to 14 mol percent CuO, about 0.8 to 1.4 mol percent of C00, and at least50 to about 52 mol percent of Fe o said material having anelectromechanical coupling coeflicient substantially exceeding 0.20.

' 3. A ferromagnetic material having piezomagnetic properties andconsisting essentially of crystals having a spinel structure and acomposition corresponding to about 29 to 47 mol percent of NiO, about 3to 20 mol percent CuO, up to about 10 mol percent Z-nO, about 0.5 to 2mol percent (300, and at least 50 to about 52 mol percent Fe O saidmaterial having an electromechanical coupling coefficient substantiallyexceeding 0.20.

4. A ferromagnetic material having piezcmagnetic properties andconsisting essentially of crystals having a spinel structure and acomposition corresponding to about 35 to 43 mol percent NiO, about 6 to14 mol percent CuO, up to about 10 mol percent ZnO, about 0.8 to 1.4 molpercent C00, and at least 50 to about 52 mol percent Fe O said materialhaving an electromechanical coupling coefiicient substantially exceeding0.20.

5. A method of making a ferromagnetic material having piezomagneticproperties comprising the steps, forming a finely-divided mixture ofabout 29 to 47 mol percent of NiO, about 2 to 20 mol percent of CuO,about 0.5 to 2 mol percent of C00, and at least 50 to about 52 molpercent of Fe O and heating said mixture in a non- -reducing atmosphereat a temperature of about 1000 to 1400 C.

6. A method of making a ferromagnetic material having piezomagneticproperties comprising the steps, forming a finely-divided mixture ofabout 29 to 47 mol percent of NiO, about 3 to 20 mol percent of CuO, upto about 10 m=ol percent of ZnO, about 0.5 to 2 mol percent of C00, andat least 50 to about 52 mol percent of Fe O and heating said mixture ina non-reducing atmosphere to a temperature of about 1000 to 1400 C.

7. A method of making a ferromagnetic material having piezomagneticpropertie comprising the steps, formlog a finely-divided mixture ofabout 29 to 47 mol per- Compcsition, mol percent Siinlter- Room temp. C.

1; P temo, N10 0110 000 F3203 C. S2 cm p Tan 5 k Qn (ring) Qstma L Qn(ring) While we have thus described our invention in connection withspecific embodiments and specific applica tions thereof, we do not Wishto be limited thereto since other modifications and applications thereofwill be readily apparent to those skilled in the art.

What we claim is:

1. A ferromagnetic material having piezomagnetic properties andconsisting essentially of crystals having a spinel structure and acomposition corresponding to about 29 to 47 mol percent of NiO, about 3to 20 mol percent of CuO, about 0.5 to 2 mol percent C00, and at least50 to about 52 mol percent of Fe Og, said material having anelectromechanical coupling coeificient substantially exceeding 0.20.

2. A ferromagnetic material having piezomagnetic cent of NiO, about 3 to20 mol percent of CuO, about 0.5 to 2 mol percent 000, and at least 50to about 52 mol percent Fe O and heating said mixture in a non reducingatmosphere to a temperature of about 1200 to 1300 C.

8. A method of making a ferromagnetic material having piezomagneticproperties comprising the steps, torming a mixture of about 29 to 47 molpercent of NiO, about 3 to 20 mol percent of CuO, up to about 10 molpercent of ZnO, about 0.5 to 2 mol percent (300, and at least 50 molpercent to about 52 mol percent -Fe O and heating said mixture in anon-reducing atmosphere to a temperature of about 1200 to 1300" C.

9. A ferromagnetic body adapted for use in a piezomagnetic vibrator andhaving an electromechanical c0upling .coefiicient substantiallyexceeding 0.20, said body consisting essentiflly of a sintered coherentbody composed of crystals having a spinel structure and a compositioncorresponding to: about 29 to 47 mol percent of NiO, about 3 to 20 molpercent of CuO, about 0.5 to 2 mol percent of C00, and at least 50 toabout 52 mol percent of Fe O 10. A ferromagnetic body adapted for use ina piezomagnetic vibrator and having an electromechanical couplingcoefiicient substantially exceeding 0.20, said body consistingessentially of a sintered coherent body composed of crystals having aspinel structure and a com position corresponding to about 29 to 47 molpercent of NiO, about 3 to 20 mol percent of CuO, up to about molpercent of ZnO, about 0.5 to 2 mol percent of C00, and at least 50 toabout 52 mol percent of F6203.

11. A ferromagnetic body adapted for use in a piezomagnetic vibrator andhaving an electromechanical coupling coefficient substantiafly exceeding0.20, said body consisting essentially of a sintered coherent bodycomposed of crystals having a spinel structure and a compositioncorresponding to about 35 to 43 mol percent of NiO, about 6 to 14 molpercent CuO, about 0.8 to 1.4 mol percent C00, and at least 50 to about52 mol percent Fe O 12. A ferromagnetic body adapted for use in apiezomagnetic vibrator and having an electromechanical couplingcoeflicient substantially exceeding 0.20, said body consistingessentially of a sintered coherent body composed of crystals having aspinel structure and a composition corresponding to about 35 to 43 molpercent of NiO, about 6 to 14 mol percent of CuO, up to about 10 molpercent of ZnO, about 0.8 to 1.4 mol percent of C00, and at least 50 toabout 52 mol percent Fe O 13. A method of making a fenromagnetic bodyadapted for use in a piezomagnetic vibrator and having anelectromechanical coupling coefiicient substantially exceedjng 0.20,comprising the steps, forming a finely-divided mixture of about 29 to 47mol percent of NiO, about 3 to 20 mol percent of CuO, about 0.5 to 2 molpercent of C00, and at least 50 to about 52 mol percent of Fe Ocompacting said mixture into a coherent body, and heating said body in anon-reducing atmosphere to a temperature of about 1000 to 1400 C.

14. A method of making a ferromagnetic body adapted for use in apiezomagnetic vibrator and having an electromechanical couplingcoefiicient substantially exceeding 0.20 comprising the steps, forming afinely-divided mix ture of about 29 to 47 mol percent of NiO, about 3 to20 mol percent of CuO, about 0.5 to 2 mol percent of C00,

and at least to about 52 mol percent of 1e 0,, compacting said mixtureinto a coherent body, and heating said body in a non-reducing atmosphereto a temperature of about 1200 to 1300 C.

1-5. A method of making a ferromagnetic body adapted for use in apiezornagnetic vibrator and having an electromechanical couplingcoeflicient substantially exceeding 020 comprising the steps, forming afinely-divided mixture of about 29 to 47 mol percent of NiO, about 3 to20 mol percent of CuO, up to about 10 mol percent of ZnO, about 0.5 to 2mol percent of C00, and at least 50 to about 52 mol percent of Fe Ocompacting said mixture into a coherent body, and heating said body in anonreducing atmosphere to a temperature of about 1000 to 1400 C.

16. A method of making a ferromagnetic body adapted for use in apiezomagnetic vibrator and having an electromechanical couplingcoeflicient substantially exceeding 0.20 comprising the steps, forming afinely-divided mixture of about 29 to 47 mol percent of NiO, about 3 to20 mol percent of CuO, up to 10 mol percent of ZnO, about 0.5 to 2 molpercent of C00, and at least 50 to about 52 mol percent of Fe Ocompacting said mixture into a coherent body, and heating said body in anon-reducing atmosphere to a temperature of about 1200 to 1300 C.

References Cited in the file of this patent UNITED STATES PATENTS2,565,861 Leverenz et a1. Aug. 28, 1951 2,640,813 Berge June 2, 19532,656,319 Berge Oct. 20, 1953 2,685,568 Wilson Aug. 3, 1954 2,723,239Harvey Nov. 8, 1955 2,736,708 Crowley et a1. Feb. 28, 1956 2,925,388Harvey Feb. 16, 1960 2,951,810 Kikuchi Sept. 6, 1960 2,989,476 EckertJune 20, 1961 3,039,966 Brockman et a1. June 19, 1962 FOREIGN PATENTS161,403 Australia Feb. 23, 1955 1,100,865 France Apr. 13, 1955 1,148,861France July 1, 1957 302,709 Switzerland Jan. 3, 1955 OTHER REFERENCESAlbers-Schoenberg: Ceramic Age, May 1952, pp. 30 and 32-35, J. Instituteof Electrical Eng, Japan, November 1937, pp. 5, 7.

1. A FERROMAGNETIC MATERIAL HAVING PIEZOMAGNETIC PROPERTIES ANDCONSISTING ESSENTIALLY OF CRYSTALS HAVING A SPINEL STRUCTURE AND ACOMPOSITION CORRESPONDING TO ABOUT 29 TO 47 MOL PERCENT OF NIO, ABOUT 3TO 20 MOL PERCENT OF CUO, ABOUT 0.5 TO 2 MOL PERCENT COO, AND AT LEAST50 TO ABOUT 52 MOL PERCENT OF FE2O3, SAID MATERIAL HAVING ANELECTROMECHANICAL COUPLING COEFFICIENT SUBSTANTIALLY EXCEEDING 0.20.